Research

Ongoing Research

Gray and harbor seals in the Northwest Atlantic have experienced relatively parallel historical population trajectories of decline following human exploitation and subsequent recovery as a result of federal protection and conservation efforts. Within the context of these ‘natural experiments’, we are studying the impacts of bottleneck and recovery on species diversity using genetic and genomic techniques. We aim to compare pre-bottleneck diversity in archaeological specimens to diversity in seal populations today from throughout the Northwest Atlantic. This work has been facilitated by several international collaborations, including with Tim Frasier, Don Bowen, Mike Hammill, the University of Maine’s Department of Anthropology, and NOAA’s Northeast Fisheries Science Center; as well as funding from an NSF Postdoctoral Fellowship in Biology.

In collaboration with local marine mammal stranding networks, Marine Mammals of Maine and Allied Whale, we are analyzing long-term datasets on marine mammal strandings throughout the state in order to better understand spatial and geographic trends in marine mammal stranding rates, distribution, and disease.

In collaboration with colleagues at the NOAA Northeast Fisheries Science Center, MIT, and WHOI, we are interested in investigating differences in disease susceptibility within and among gray and harbor seals in the North Atlantic. Our region has experienced multiple unusual mortality events attributed to infectious disease epidemics in harbor seals, yet gray seals appear relatively resistant to both phocine distemper virus and influenza A virus.

Recent Research

Harmful algal blooms (HABs), or red tides, of Karenia brevis occur almost annually in the Gulf of Mexico and threaten coastal ecosystems, including coastal and estuarine bottlenose dolphin populations. Since 1999, four large-scale bottlenose dolphin die-offs have been associated with these toxic blooms. Interestingly, dolphin populations appear to differ in susceptibility to mortality due to HAB exposure. We used candidate gene and genomic approaches to investigate a genetic basis for this susceptibility in dolphins from central-west Florida, where dolphins appear relatively resistant to HABs, and the Florida Panhandle, where dolphins appear relatively susceptible. The candidate gene approach characterized variation at a family of immune system genes (MHC) and the biological target of the HAB toxin (voltage-gated sodium channels). The genomics approach used restriction site-associated DNA (RAD) sequencing to assess variation at thousands of single nucleotide polymorphisms (SNPs) across the bottlenose dolphin genome.

Pagophilic seals, such as harp seals, are indicator species for the health of high-latitude ecosystems experiencing rapid declines in sea ice cover due to climate change. We analyzed the effect of ice cover, in combination with demographics and genetic diversity, on harp seal stranding rates along the eastern coast of the United States. Using microsatellites, we found high overall genetic diversity in the harp seal population and no difference between stranded seals and by-caught seals, which represented the healthy population. Yearly variation in harp seal stranding rates could be partially explained by sea ice cover; a greater number of harp seal strandings, particularly of male yearlings, occurred in years with low sea ice cover.

Gray seal breeding colonies experience high levels of pup mortality due to infection. We investigated geographic variation in an immune system gene, the major histocompatibility complex (MHC), among gray seal breeding colonies around the United Kingdom and found patterns of variation consistent with habitat-specific selection on the MHC in gray seals. Mortality rates in gray seals vary among breeding colony habitat types (e.g., sandy beaches vs. inland pools), which suggests environmental variation in pathogen pressure that may drive local immunogenetic adaptation.